In a known form of electro-mechanical position indicator, two parts are movable relative to one another in a predetermined direction. One part is provided with a primary winding so arranged that with an alternating current supplied thereto, an alternating magnetic flux is generated substantially normal to the direction of movement referred to, this magnetic flux varying in a predetermined manner at least in this direction. The other part of the position indicator is provided with at least two sensing windings mutually offset in the aforesaid direction. These sensing windings each sense the magnetic flux in proximity thereto.
Rotary devices of the type described in the preceeding paragraph are particularly useful in measuring angles. One form of such a device is a conventional resolver, which characteristically includes two sensing windings disposed relative to one another at an angle of 90.degree.. A further such device is a conventional synchro, which characteristically includes three windings that are mutually displaced by 120.degree.. Resolvers and synchros are normally used for transmitting data representing angles from a transmitting device to a receiving device and continuous or continual angular transmission can be provided. Other forms of resolvers and synchros can be used as angle-measuring devices, particularly where an accuracy is desired which is greater than that provided by resolvers and synchros which are now commercially available. Such angle-measuring devices could be used to measure angles with the degree of accuracy required, for example, for theodolites or gun-sights, etc. In such applications, a device is normally used in which an accurately prepared measuring pattern is placed on, for example, sheets of glass or some other stable material and read off optically or electronically. In order to eliminate the effect of parallax, for example, a reading has been made at two or more positions. The number of positions such readings require increases with the number of parts of the pattern read off, thus lowering the accuracy requirements of an individual marking of the measuring pattern.
Since angle-measuring devices of the aforementioned optical type must be manufactured with a very high degree of accuracy, the devices are extremely expensive. Such devices are also very fragile.
In the case of a conventional electro-mechanical resolver or synchro, the whole of the mutually movable surfaces are used for the detection of an angle, since the magnetic field which transfers the angular information between stator and rotor often varies in the manner of a sine or cosine fuction over the surface in question. The stability of such a component can therefore be less with respect to each individual "electrical loop" of the emitter winding since the output signal of the angle indicator (resolver or synchro) constitutes the mean value of the position of a large number of loops. If the individual loops could be fixed in a stable, accurate manner, a resolver or a synchro would be an extremely accurate angle-indicator. There is a further problem, however, with the use of a conventional electro-mechanical resolver or synchro as an angle measuring device. This problem results from the fact that such an electromechanical device includes a multiplicity of lamellae which are joined together with other elements. This makes it difficult to thermally match the elements incorporated in the device, so that changes in temperature will affect the output signal. The effect of temperature variations can cause measuring variations of the order of magnitude of several minutes of arc.